In Japan, two standard-time wave signals of 40 kHz and 60 kHz, each containing time data, i.e., a time code, are transmitted at present from two transmission stations (in Fukushima and Saga Prefectures). FIG. 9 shows the format of the time code contained in these standard-time wave signals.
The time code shown in FIG. 9 is transmitted every minute, in the form of a 60-second frame. The code has a start marker (M) that indicates the start time (i.e., the 0th second of any minute) of the 60-second frame. The startmarker (M) has a pulse width of 0.2 seconds. The code also has position markers having a pulse width of 0.2 seconds. The position markers are arranged at the 9th second (P1), the 19th second (P2), the 29th second (P3), the 39th second (P4), the 49th second (P5), and the 59th second (P0), respectively. Thus, two markers, i.e., one start marker (M) and one position marker (P0), each having a pulse width of 0.2 seconds, are arranged at the boundary between any two adjacent frames. The start of a new frame can be recognized from these two markers. The start marker (M) is the frame reference marker (M). The leading edge of the pulse represented by the frame reference marker (M) is the accurate time of updating the minute-place of the current time. In the frame, the data items representing the minute, hour and day (counted from January 1), year (the lowest two digits of the Christian era), day of the week, and the like are arranged in the 0th to 9th second bracket, the 10th to 19th second bracket, and 30th to 40th second bracket, each in the form of binary-coded decimal numbers. In this case, logic 1 and logic 0 are represented by a pulse having a width of 0.5 seconds and a pulse having a width of 0.8 seconds, respectively. Note that the frame shown in FIG. 9 indicates the data representing 17:25 of the 114th day of the year.
In recent years, so-called radio-wave clocks have come into practical use. A radio-wave clock receives a standard-time wave signal containing such a time code as described above. In the clock, the signal is used to correct the time data set in the time-measuring circuit. The radio-wave clock incorporates an antenna, which receives standard-time wave signals at predetermined intervals. Each signal received is amplified and modulated. The time code contained in the signal is decoded and used to correct the time data set in the time measuring circuit.
Electronic-wave clocks of this type are installed usually in rooms. If they are installed in steel-framed houses or in the basement, they cannot receive standard-time wave signals in many cases. To solve this problem, a system has been proposed, as disclosed in Jpn. Pat. Appln. Laid-Open Publication No. 2000-75064. In the system, a relay device is provided that receives standard-time wave signals and modulates the time code contained in each wave signal with a predetermined carrier wave, and transmits the wave signals each containing a modulated time code to the radio-wave clock. The time code is used to correct the time data set in the clock.
When the radio-wave clock is near the relay device, however, there layed wave signal it receives is too intensive. Therefore, the clock cannot receive the time code in normal way. Consequently, an error may occur in correcting the time data set in the radio-wave clock.